1. Field of the Invention
This invention relates to a process for the manufacture of impact resistant thermoplastic molding materials. More particularly this invention relates to a process of making acrylic ester-modified styrene-acrylonitrile terpolymer which are modified to be impact resistant, ASA, and acrylonitrile-butadiene-styrene, ABS, polymers by graft polymerization using an agglomerated rubber latex which was produced in emulsion.
2. Description of the Prior Art
The following references are part of the current state of the art: (1) German Application No. 24 27 960, (2) German Application No. 12 47 665, (3) German Application No. 12 69 360, (4) German Application No. 13 00 241 and (5) German Application No. 12 92 850.
The rubber latices which are produced by the commonly used homo- or mixed polymerization of, for instance, butadiene in emulsion have particle diameters in the order of magnitude of approximately 0.02 to 0.15 microns. ABS and ASA polymers which are produced with such rubbers show a relatively low impact resistance. It is known that ABS polymers with more favorably properties can be produced if rubber latices with larger particles are used for the grafting polymerization.
References (2) and (3) relate to butadiene polymer latices having particle sizes of 0.15 to 0.6 microns and/or a latex particle diameter of more than 0.3 microns. In these references, statements are also made as to how such large particle latices are obtained, for instance, by polymerization in concentrated emulsion, by using smaller amounts of emulsifier, or by staggering the addition of emulsifier. These direct polymerization processes for the manufacture of coarse particle latices, however, have the drawback of relatively long polymerization times: Generally it takes several days for achieving essentially complete reaction.
Another direct method for the manufacture of coarse particle latices is recommended in reference (3). According to this method, additional monomers are to be added during the polymerization. This process also requires long polymerization times.
An indirect method for the manufacture of coarse particle latices consists of adding electrolytes to a fine particle rubber latex thereby enlarging the particles, compare reference (5). In accordance with this method, the agglomeration takes place during the grafting process. This method has two drawbacks: because of the danger of coagulation, larger quantities of emulsifier must be added which may result in disturbances during the subsequent precipitation. In addition to this, the added ions partially remain in the product and can result in corrosion during processing and can further cause a discoloration of the product.
In addition to this, a number of physical methods for agglomeration, for instance, freezing or shear agglomeration, as well as additional chemical methods, for instance, the agglomeration with polymer dispersions based on polyvinyl ethers are cited as the current state of the art in reference (1).
In reference (1) a process for the manufacture of coarse particle suspension is described wherein the agglomeration is implemented by adding an acrylate polymer dispersion to the rubber latex.
The drawback of this process is that a relatively large amount of coagulate is incurred after the graft polymerization.
A purpose of this invention was to develop a process according to which the particles of a rubber latex can be partially or entirely agglomerated in a simple and industrially economically implementable manner such that this process can be used to manufacture ABS and/or ASA polymers with a balanced property combination of impact resistance, flowability and surface gloss and the amount of coagulate during the manufacture of the dispersion being reduced.
This purpose is met by a process for the manufacture of impact resistant thermoplastic molding materials comprising
I. polymerization of at least one monomer selected from the group consisting of
(a) conjugated diolefins having 4 carbon atoms to 5 carbon atoms, PA1 (b) acrylates of alcohols having 1 carbon atom to 8 carbon atoms, PA1 (c) comonomers of (a) or (b) and PA1 (d) monomers having a cross-linking action in the presence of water PA1 (e) at least one emulsifier and PA1 (f) at least one initiator to produce a rubber latex having an average particle size (d.sub.50 -value of the integral mass distribution) in the range of 0.02 to 0.15 micron, PA1 (g) acrylate polymer dispersions and PA1 (h) polyvinylether dispersions, in such a manner that an average particle size (d.sub.50 -value of the integral mass distribution) of 0.20 to 0.65 micron is obtained, and
and in the presence of
II. addition of at least one chemically acting agglomeration agent selected from the group consisting of
III. graft polymerization of 20 to 90 percent by weight of at least one monomer selected from the group consisting of styrene, acrylonitrile, methylmethacrylate and mixtures thereof optionally with monomers having a cross-linking action in the presence of 80 to 10 percent by weight of the agglomerated rubber latex of step II relative to the solid material wherein potassium salts of saturated or unsaturated fatty acids having 10 to 30 carbon atoms are used as emulsifier (e).